The proposed research will investigate the role of new islet autoantibodies, HLADQ high risk haplotypes and a novel potential T1DM susceptibility genetic locus (polymorphism of the gene ICA1) in risk of conversion to T1DM in the largest population based cohort of first degree relatives of T1DM patients, with and without T1DM, from the same geographical area. Small sample sizes, limited follow-up and the lack of advanced technology have limited previous studies in this field. In this competitive renewal, it will be possible to determine the risk of conversion to T1DM utilizing new islet biochemical islet autoantibody assays in this specific population. Recent data indicate that the most popular screening assays for detecting islet autoantibodies are not sufficient for predicting T1DM. Over the past few years, molecular cloning techniques have been applied to identify T1DM-related targets of islet autoimmunity. We now provide preliminary data suggesting that diabetes the progression rate can be increased to nearly 100% with the addition of two novel assays detecting autoantibodies to IA-2 Fragment 1 (aa residues 761- 964) and IA-2ic (aa residues 601-979). To increase sensitivity, in collaboration with Drs. Hampe and Lernmark of the University of Washington, we plan to apply autoantibodies recognizing specific epitopes of the antigen GAD65 in combination with the conventional islet autoantibody markers. Two HLA-DQ high-risk haplotypes and SNPs within the ICA1 locus (encoding the antigen ICA69) will also be evaluated as risk factors for insulin-requiring diabetes. This research will be performed at the Pittsburgh center, which currently has 123 first degree relatives, who converted to insulin-requiring diabetes during follow-up (converters), from a pool of over 7,000 relatives of T1DM probands. Approximately 140 converters should be available by the end of this grant period. This represents the largest number of converters for any center. Also, DNA has been collected from relatives of T1DM patients, and we have specimens on complete singleton and multiplex families in our repository with affected and unaffected siblings. This is a unique set of serum and DNA samples for the testing of immunologic and genetic hypotheses. The outcome of the proposed investigation should facilitate the stage for the application of a new screening strategy based upon the use of IA-2 and GAD65 epitope markers in combination with conventional islet autoantibody testing that could be of benefit in major clinical trials aimed at evaluating new approaches for understanding, preventing, and treating Type 1 diabetes.